1. Field of the Invention
The present invention relates to an oxide superconductor which excels at magnetic properties, mechanical strength and resistance to environment, and to a method of manufacturing such an oxide superconductor. Further, the present invention is applicable to, for example, a current lead, magnetic bearings, a magnetic shielding and a bulk magnet.
2. Description of the Related Art
Hitherto, there has been known a conventional method of manufacturing such a kind of an oxide superconductor (see Japanese Unexamined Patent Publication (Kokai) No. Hei 5-193938/1993 Official Gazette), by which a RE--Ba--Cu--O oxide superconductor (incidentally, RE denotes one or more kinds of rare earth elements including Y) is manufactured by bringing a seed crystal into contact with a raw material mixture, which contains a RE compound, a Ba compound and a Cu compound, and causing the growth of a crystal from the seed crystal after the heating of the raw material mixture to a temperature, which is not lower than the melting point thereof, and the melting thereof.
In the case of the conventional method described in this Official Gazette, a single crystal of a REBa.sub.2 Cu.sub.3 O.sub.7-X phase (hereunder sometimes referred to as a "123 phase") is used as a seed crystal. In accordance with this conventional method, crystal growth from the seed crystal is enabled by using one or more RE elements composing the "123 phase" of a superconductor to be produced, which are different from those of the seed crystal, and selecting one of the combinations of such RE elements in such a manner that the "123 phase" formation or forming temperature of the seed crystal is higher than the "123 phase" formation temperature of the superconductor to be produced.
However, in the case of the aforementioned manufacturing method, it is necessary to select RE elements in such a way that the "123 phase" formation temperature of the seed crystal is higher than the "123 phase" formation temperature of the superconductor to be manufactured. This is because of the fact that after crystallization, lattice contraction occurs in the material of this seed crystal owing to the increasing or reducing of oxygen (content) and microcracks extending in a direction perpendicular to the c-axis are produced. It is difficult to cut an elongated seed crystal therefrom and the seed crystal melts unless there is established a large difference in crystallization temperature between the seed crystal and the superconductor to be produced. As an inevitable consequence, this conventional method cannot be applied to the case of manufacturing a superconductor that employs a RE element, which has the highest "123 phase" formation temperature, as a composing element. This is because no seed crystal having the "123 phase", whose formation temperature is higher than the highest "123 phase" formation temperature of such a superconductor, can be prepared.
Moreover, even in the case of manufacturing a superconductor that employs a RE element, which has the highest "123 phase" formation temperature, as a composing element, the difference in the formation temperature between the seed crystal and the superconductor is small, so that the advantageous effect of this conventional method utilizing the difference in the formation temperature therebetween is not obtained.
The present invention is accomplished to solve the aforementioned problem of the conventional method.